Beta-decay stable isobars


Beta-decay stable isobars are the set of nuclides which cannot undergo beta decay, that is, the transformation of a neutron to a proton or a proton to a neutron within the nucleus. A subset of these nuclides are also stable with regards to double beta decay or theoretically higher simultaneous beta decay, as they have the lowest energy of all nuclides with the same mass number.
This set of nuclides is also known as the line of beta stability, a term already in common use in 1965. This line lies along the bottom of the nuclear valley of stability.

Introduction

The line of beta stability can be defined mathematically by finding the nuclide with the greatest binding energy for a given mass number, by a model such as the classical semi-empirical mass formula developed by C. F. Weizsäcker. These nuclides are local maxima in terms of binding energy for a given mass number.
βDSOneTwoThree
2-3417
36-5857
60-7252
74-1162191
118-1542116
156-192514
194-21063
212-262719
Total49757

All odd mass numbers have only one beta decay stable nuclide.
Among even mass number, seven have three beta-stable nuclides. None have more than three, all others have either one or two.
All primordial nuclides are beta decay stable, with the exception of 40K, 50V, 87Rb, 113Cd, 115In, 138La, 176Lu, and 187Re. In addition, 123Te and 180mTa have not been observed to decay, but are believed to undergo beta decay with an extremely long half-life. All elements up to and including nobelium, except technetium and promethium, are known to have at least one beta-stable isotope.

List of known beta-decay stable isobars

350 beta-decay stable nuclides are currently known. Theoretically predicted or experimentally observed double beta-decay is shown by arrows, i.e. arrows point towards the lightest-mass isobar.
No beta-decay stable nuclide has proton number 43 or 61 and no beta-decay stable nuclide has neutron number 19, 21, 35, 39, 45, 61, 71, 89, 115, 123, or 147.
Even NOdd N
Even ZEven AOdd A
Odd ZOdd AEven A

Odd AEven AOdd AEven AOdd AEven AOdd AEven A
1H2H3He4He5He 6Li7Li8Be
9Be10B11B12C13C14N15N16O
17O18O19F20Ne21Ne22Ne23Na24Mg
25Mg26Mg27Al28Si29Si30Si31P32S
33S34S35Cl36S ← 36Ar37Cl38Ar39K40Ar ← 40Ca
41K42Ca43Ca44Ca45Sc46Ca → 46Ti47Ti48Ca → 48Ti
49Ti50Ti ← 50Cr51V52Cr53Cr54Cr ← 54Fe55Mn56Fe
57Fe58Fe ← 58Ni59Co60Ni61Ni62Ni63Cu64Ni ← 64Zn
65Cu66Zn67Zn68Zn69Ga70Zn → 70Ge71Ga72Ge
73Ge74Ge ← 74Se75As76Ge → 76Se77Se78Se ← 78Kr79Br80Se → 80Kr
81Br82Se → 82Kr83Kr84Kr ← 84Sr85Rb86Kr → 86Sr87Sr88Sr
89Y90Zr91Zr92Zr ← 92Mo93Nb94Zr → 94Mo95Mo96Zr → 96Mo ← 96Ru
97Mo98Mo → 98Ru99Ru100Mo → 100Ru101Ru102Ru ← 102Pd103Rh104Ru → 104Pd
105Pd106Pd ← 106Cd107Ag108Pd ← 108Cd109Ag110Pd → 110Cd111Cd112Cd ← 112Sn
113In114Cd → 114Sn115Sn116Cd → 116Sn117Sn118Sn119Sn120Sn ← 120Te
121Sb122Sn → 122Te123Sb124Sn → 124Te ← 124Xe125Te126Te ← 126Xe127I128Te → 128Xe
129Xe130Te → 130Xe ← 130Ba131Xe132Xe ← 132Ba133Cs134Xe → 134Ba135Ba136Xe → 136Ba ← 136Ce
137Ba138Ba ← 138Ce139La140Ce141Pr142Ce → 142Nd143Nd144Nd ← 144Sm
145Nd146Nd → 146Sm 147Sm 148Nd → 148Sm ← 148Gd 149Sm150Nd → 150Sm ← 150Gd 151Eu 152Sm ← 152Gd
153Eu154Sm → 154Gd ← 154Dy 155Gd156Gd ← 156Dy157Gd158Gd ← 158Dy159Tb160Gd → 160Dy
161Dy162Dy ← 162Er163Dy164Dy ← 164Er165Ho166Er167Er168Er ← 168Yb
169Tm170Er → 170Yb171Yb172Yb173Yb174Yb ← 174Hf 175Lu176Yb → 176Hf
177Hf178Hf179Hf180Hf ← 180W 181Ta182W183W184W ← 184Os
185Re186W → 186Os 187Os188Os189Os190Os ← 190Pt 191Ir192Os → 192Pt
193Ir194Pt195Pt196Pt ← 196Hg197Au198Pt → 198Hg199Hg200Hg
201Hg202Hg203Tl204Hg → 204Pb205Tl206Pb207Pb208Pb
209Bi 210Po 211Po 212Po ← 212Rn 213Po 214Po ← 214Rn 215At 216Po → 216Rn
217Rn 218Rn ← 218Ra 219Fr 220Rn → 220Ra 221Ra 222Ra 223Ra 224Ra ← 224Th
225Ac 226Ra → 226Th 227Th 228Th 229Th 230Th ← 230U 231Pa 232Th → 232U
233U 234U 235U 236U ← 236Pu 237Np 238U → 238Pu 239Pu 240Pu
241Am 242Pu ← 242Cm 243Am 244Pu → 244Cm 245Cm 246Cm 247Bk 248Cm → 248Cf
249Cf 250Cf 251Cf 252Cf ← 252Fm 253Es 254Cf → 254Fm 255Fm 256Cf → 256Fm
257Fm 258Fm ← 258No 259Md 260Fm → 260No 262No -

All beta-decay stable nuclides with A ≥ 209 were observed to decay by alpha decay except some where spontaneous fission dominates. With the exception of 262No, no nuclides with A ≥ 260 have been definitively identified as beta-stable, although 260Fm and 262No are unconfirmed.
The general patterns of beta-stability are expected to continue into the region of superheavy elements, though the exact location of the center of the valley of stability is model dependent. It is widely believed that an island of stability exists along the beta stability line for isotopes of elements around copernicium that are stabilized by shell closures in the region; such isotopes would decay primarily through alpha decay or spontaneous fission. Beyond the island of stability, various models that correctly predict the known beta-stable isotopes predict anomalies in the beta-stability line that are unobserved in any known nuclides, such as the existence of two beta-stable nuclides with the same odd mass number. This is a consequence of the fact that a semi-empirical mass formula must consider shell correction and nuclear deformation, which become far more pronounced for heavy nuclides.

Beta decay toward minimum mass

Beta decay generally causes isotopes to decay toward the isobar with the lowest mass with the same mass number, those not in italics in the table above. Thus, those with lower atomic number and higher neutron number than the minimum-mass isobar undergo beta-minus decay, while those with higher atomic number and lower neutron number undergo beta-plus decay or electron capture. However, there are four nuclides that are exceptions, in that the majority of their decays are in the opposite direction:
Chlorine-3635.96830698Potassium-4039.96399848Silver-108107.905956Promethium-146145.914696
2% to Sulfur-3635.9670807611.2% to Argon-4039.96238312253% to Palladium-108107.90389237% to Samarium-146145.913041
98% to Argon-3635.96754510689% to Calcium-4039.9625909897% to Cadmium-108107.90418463% to Neodymium-146145.9131169